This a new medicinal chemistry application designed to determine the structure-activity relationships for a range of cysteine proteinases and to apply these findings to develop new reagents for purifying cysteine proteinases by kcat chromatography. Several of the methods are based on extensive preliminary studies carried out in collaboration with Dr. A. J. Barrett of Strangeways Research Laboratory at Cambridge UK and this collaboration will continue. Computerized molecular modeling will be used to collate the structure-activity data in molecular terms and to guide the design of new inhibitors and new affinity resins. The cysteine proteinases are a class of enzyme, only recently discovered to be involved in many important biological processes. Selective inhibition of certain cysteine proteinases could form the basis for treatments of osteoporosis, arthritis, and other chronic diseases. Specific objectives include: Determine the structure-activity relationships for new peptidyl semicarbazones, aldehydes, and nitriles for inhibition of the following cysteine proteinases: papain; cathepsin B, H, and L; the cysteine proteinase for entamoeba histolytica; and calpains I and II. Synthesize novel cyclic inhibitors that link the P1 and P3 inhibitor side chains to probe the bioactive conformation of these inhibitors when bound to different cysteine proteinases. Develop new kcat affinity chromatography resins for purifying the above cysteine proteinases and additional new cysteine proteinases as they are discovered. Synthesize new E-64 and Ep-475 derivatives designed to identify the site of alkylation on the inhibitor by the enzyme by using 13C NMR. Synthesize new types of inhibitors designed to span both the P and P prime (P') binding sites of proteinases. Use computerized molecular modeling methods of X-ray crystal structures of papain, actinidin to evaluate the results obtained and to predict new structures for synthesis. Develop a 3- dimensional model for the human cysteine proteinases, cathepsin B, H, and L, for which X-ray crystal structures are not available.